Blood examinations are the most common procedure for medical checkups. In recent years, technological developments for performing blood examinations on microchips have been advanced. Thus, by using such an on-chip system, there have been expectations in reducing pain from blood sampling with a decrease in the required blood amount, downsizing apparatuses, speeding up examinations through point-of-care testing and reducing examination costs by decreasing reagent amounts, etc.
Meanwhile, most examination items in blood examinations are associated with soluble components in blood, and the blood cells which occupy approximately 50% volume in the blood are components which hinder these examinations. Thus, prior to an examination, it is required to acquire only blood plasma by separating blood plasma from the blood cells.
In conventional methods, a method of using a filter, a method of precipitating the blood cells by a centrifuge and a method of coagulating the blood cells by adding an agent, and the like have been adopted for this blood plasma separation. It is conceivable that these methods are also applied when a blood examination is performed on the microchip.
For example, in Patent Document 1, an analysis chip for separating blood cells using a porous body for a pretreatment element has been disclosed.
Also in Patent Documents 2 and 3, it has been proposed that blood components are separated by a gravitational force in a process where the blood is continuously flown. For example, in an apheresis system having a sealed container 101 shown by a partial cross section perspective view in FIG. 12, the blood to which an anticoagulant has been added is passed through an introduction path 103 and introduced from a blood introduction inlet 103a to one of the blood channels 102 continuously. As the blood is flown along the blood channel 102, the blood is separated into a supernatant layer 104 composed of blood plasma containing rich platelets and a precipitation layer 105 composed of the blood cells such as erythrocytes and leukocytes. And, at an end of a downstream of the blood channel 102, the blood plasma containing the rich platelets in the supernatant layer 104 is discharged from a discharge path 106 by passing through a discharge outlet 106a provided at the shallowest site. The blood cells in the precipitation layer 105 are discharged from a discharge path 107 by passing through a discharge outlet 107a provided at the deepest site. For example, the volume of the blood channel 102 is approximately 300 mL, and the blood introduced at a flow volume of approximately 20 mL/minute is separated in a residence time of approximately 15 minutes in the sealed container 101.
Patent Document 1: Japanese Published Unexamined Patent Application No. 2006-58280
Patent Document 2: Japanese Published Unexamined Patent Application No. S57-131451
Patent Document 3: Japanese Published Unexamined Patent Application No. S58-41822